1. Field of the Invention
This invention relates to data packet switching systems and, more particularly, to combined time-division and space-division switching systems for data packets.
2. Description of the Prior Art
Packet transmission of data is an efficient method of time-sharing the capacity of a transmission line among several streams of data. A packet is formed by combining data characters from a single data communication conversation with a header containing address information. When data transmission is bursty, the packets of one conversation may efficiently share a single transmission facility with those of other conversations. The packets of the several conversations are interleaved in time, taking advantage of the idle times between bursts of transmission in each of the several conversations. The data packets belonging to several conversations are transmitted independently of each other, each routed by the address information in its packet header.
Data packets must be switched at transmission branching points. As each packet enters a switch, it is routed to an outgoing transmission line selected on the basis of the address information in the packet header. Time-division packet switches have traditionally accomplished this by merging onto a single buss the packets from all incoming transmission lines. From that single buss, the packets are then redistributed to the several outgoing transmission lines. It can thus be seen that a time-division packet switch is a switch in which many users utilize the same physical facility (the buss) at different times.
Modern data transmission requirements suggest the need for large switches capable of handling traffic from a very large number of transmission lines. In this case, the limited capacity of a single time-division buss becomes a constraint on the capabilities of the switch. An alternative design for a packet switch is therefore required which has no such constraint.